Headphones and other physical configurations of personal ANR device worn about the ears of a user for purposes of isolating the users ears from unwanted environmental sounds have become commonplace. In particular, ANR headphones in which unwanted environmental noise sounds are countered with the active generation of anti-noise sounds have become very prevalent, even in comparison to headphones or ear plugs employing only passive noise reduction (PNR) technology, in which a users ears are simply physically isolated from environmental noise sounds.
Unfortunately, despite various improvements made over time, existing personal ANR devices continue to suffer from a variety of drawbacks, especially in environmental situations that tend to reduce the effectiveness of feedforward-based ANR. Where a microphone is incorporated into an ANR device as a feedforward microphone such that it is acoustically coupled to the surrounding environment to detect noise sounds as a reference input for feedforward-based ANR, instances of wind noise, noise transmitted through the structure of the ANR device to the feedforward microphone, and/or occlusions physically blocking the access of the feedforward microphone to the surrounding environment can defeat the effectiveness of the feedforward-based ANR. Especially in instances of wind noise and noise transmitted through structure, the feedforward microphone can be subjected to noises that are not correlated with any acoustic noise present within an earpiece of the ANR device.
More particularly, wind noise commonly arises when a flow of air in the surrounding environment generates one or more vortices in the vicinity of a microphone such that a diaphragm of the microphone is variously pushed and pulled by changes in air pressure occurring only in the vicinity of the microphone. Thus, the microphone detects the sounds of these highly localized vortices (often perceived as a “rumbling” sound) in addition to detecting environmental noise sounds, and the electrical output of the microphone is a signal representing this combination of sounds. Where such a microphone is employed as a feedforward microphone to provide reference noise sounds for the generation of feedforward anti-noise sounds, circuitry employed to generate those feedforward anti-noise sounds attempts to generate anti-noise sounds from the environmental noise sounds and the sounds of those highly localized vortices. Unfortunately, since those vortices are so very localized to the vicinity of the feedforward microphone, there are no acoustic noises within an earpiece of the ANR device that are correlated to the sounds of the vortices for the anti-noise sounds generated from the sounds of those vortices to interact with and attenuate. As a result, the anti-noise sounds generated from the sound of those vortices actually become additional noise sounds generated by the feedforward circuitry and acoustically output within the earpiece, such that the feedforward-based ANR function of the ANR device may actually generate more noise than it attenuates.
Further, occlusions blocking access to the surrounding environment can have a “muffling” effect such that environmental noise sounds reaching the feedforward microphone can be greatly attenuated. This muffling effect can also attenuate environmental noise sounds at different frequencies to different degrees. Thus, any circuit generating feedforward anti-noise sounds may be provided a signal from the feedforward microphone that represents an attenuated and/or distorted form of the environmental noise sounds that the feedforward microphone would have otherwise detected, thereby resulting ultimately in poorer noise attenuation.